This invention relates to electro-pneumatic converters (sometimes called electro-pneumatic "regulators") and has particular reference to such converters commonly referred to as I/P ("I to P") converters.
I/P converters are used to control pneumatic pressure--usually of compressed air--in response to the electrical output of an electronic control source. The common industry standard for the electronic control source is that the output current should preferably vary in the range 4-20 mA with 4 mA corresponding to minimum pressure and 20 mA to maximum pressure.
Electro-pneumatic converters may either fail to zero (otherwise called "fail safe") when the current is, for whatever reason, cut off, or may fail to a freeze condition or to another pressure predetermined by the user. In a fail to zero converter, with which the invention is particularly, but not exclusively, concerned the absence of current results in the pressure in the output line falling to a low, typically atmospheric pressure.